Touch technology provides people with a more humanized operation manner of human-computer interaction, and has gradually grown as a dominant manipulation technique. Touch screen technologies, which were invented in the 1970s and have been developed for over 40 years, generally include four categories depending on the type of the used sensor, that is, a capacitive touch screen, a resistive touch screen, an infrared touch screen, and an acoustic wave touch screen, among which, the capacitive touch screen has the largest market share of the touch screen field due to its advantages such as multi-touch, accurate positioning, and long lifetime. Most of the present capacitive touch screens are of an on-cell structure, in which the touch panel and the display panel are two independent devices directly superimposed on each other for assembly. Such a manner that the touch panel is directly attached onto the display panel inevitably adds the thickness and weight of the touch panel to the display unit, and thus does not meet the requirements of lighter and thinner display devices in the present market. Furthermore, the touch panel has relatively numerous layers and thus decreases light transmittance, thereby adversely affecting a display effect of the display device.
The in-cell capacitive touch screen is such that various film layers are made between the upper and lower glass substrates so that a touch layer is embedded in the color filter substrate, thus one glass substrate can be saved compared with the externally-attached structure, and an additional protection layer for protecting sensing units of the capacitive touch screen is not required. Therefore, the light transmittance and the display effect of the screen are greatly improved while reducing manufacturing process steps and costs, the manufacturing process is relatively simple and suitable for mass production, and the capacitive touch screen display is made lighter and thinner and satisfies requirements for portability and lightweight of the handheld device.
As shown in FIG. 1, an in-cell capacitive touch screen in the prior art generally includes: a Thin Film Transistor (TFT) substrate 101, as well as a circuit electrode 101a, a liquid crystal layer (not shown), a color filter (CF) substrate 102, a black matrix (not shown), a touch layer 103, a color resistance layer (not shown), and an insulating layer 104 located on the TFT substrate 101. Drive lines and sense lines, which are arranged across with each other, are arranged on the touch layer 103.
As shown in FIG. 2, a touch signal is generated when a finger touches an intersection of a drive line with a sense line. The detection principle of the screen includes: applying driving signals on the drive lines, and detecting a signal change on the sense lines. Assuming that the drive lines are used to determine X-direction coordinates and the sense lines are used to determine Y-direction coordinates, in the process of the detection, the drive lines in the X direction are progressively scanned, and the signal on each sense line is read in scanning each drive line, thus, each of intersections of all the sense lines with all the drive lines can be traversed within a cycle of scanning, so as to determine the intersection on which a touch action is performed.
FIG. 3 shows an equivalent circuit diagram at the intersection of the drive line and the sense line, a mutual capacitor C is equivalently coupled at each intersection and has a capacitance which is the sum of a facing capacitance formed at the overlap between the drive line and the sense line and an edge capacitance formed by the patterned edges on the sense line and the drive line; a resistor Rt denotes the equivalent resistor of the drive line, a resistor Rr denotes the equivalent resistor of the sense line; a parasitic capacitor Ct is formed on the drive line and a parasitic capacitor Cr is formed on the sense line; an excitation source is used to generate the driving signal Vin; and the touch detection circuit is an amplifier, which is configured to convert the electrical signal on the sense line into a voltage signal Vout for outputting. When a finger touches the screen, the finger functions as a bridge between the drive line and the sense line at the touch contact, which is equivalent to connect a further capacitor in parallel with the mutual capacitor C, causing the capacitance of the mutual capacitor C to increase, leading to a change of the electrical signal on the sense line, and thus generating a change in the output voltage Vout. In conjunction with FIG. 3, during the operation of the in-cell capacitive touch screen, a liquid crystal is rotated by a different angle for displaying different gray scale pictures, thus the liquid crystal capacitor Clc has a different capacitance, which leads to a different change in the output voltage Vout. Therefore, the noise generated by the rotation of the liquid crystals likely interferes and impacts the touch sensing signal in the touch layer, thus causing an inaccurate touch contact detection, which may cause a malfunction of the touch screen.